TRANSFORMATIONS, LIFETIMES, AND SOURCES OF NO2, HONO, AND HNO3 IN INDOOR ENVIRONMENTS

Recent research has demonstrated that nitrogen oxides are transformed to nitrogen acids in indoor environments, and that significant concent rations of nitrous acid are present in indoor air. The purpose of the study reported in this paper has been to investigate the sources, chem ical transformations and lifetimes of nitrogen oxides and nitrogen aci ds under the conditions existing in buildings. An unoccupied single fa mily residence was instrumented for monitoring of NO, NO2, NO(y), HONO , HNO3, CO, temperature, relative humidity, and air exchange rate. For some experiments, NO2 and HONO were injected into the house to determ ine their removal rates and lifetimes. Other experiments investigated the emissions and transformations of nitrogen species from unvented na tural gas appliances. We determined that HONO is formed by both direct emissions from combustion processes and reaction of NO2 with surfaces present indoors. Equilibrium considerations influence the relative co ntributions of these two sources to the indoor burden of HONO. We dete rmined that the lifetimes of trace nitrogen species varied in the orde r NO is similar to HONO > NO2 > HNO3. The lifetimes with respect to re active processes are on the order of hours for NO and HONO, about an h our for NO2, and 30 minutes or less for HNO3. The rapid removal of NO2 and long lifetime of HONO suggest that HONO may represent a significa nt fraction of the oxidized nitrogen burden in indoor air.